1. Field of the Invention
This invention relates generally to high intensity discharge (HID) headlamps for vehicles and in particular to an apparatus and method for causing an HID headlamp to flicker when operating in a vehicle because it does not belong in that particular vehicle.
2. Description of Related Art
In a high intensity discharge bulb, a high voltage is passed through a metallic salt. The metallic salt in a sealed container becomes gaseous, passing an electrical arc. The illumination given off by the arc is initialized for headlamps. HID headlamps have several advantages over incandescent bulb headlamps as described in U.S. Pat. No. 5,709,451 issued to Flora et al. in 1998. One advantage is that the HID bulb gives off a blue-tinted light which is closer to natural sunlight and illuminates phosphorous signs better, making them stand out more at night. Another advantage of HID headlamps is that they consume less electrical energy, are more reliable, and give off less heat, thereby giving more flexibility in the design of the reflector housing and other items packaged near the headlamp. Conventional automotive applications of HID headlamps are disclosed in U.S. Pat. No. 5,180,218 issued to Ohshio in 1993.
Because of the advantages of HID headlamps and the fact that they are more costly than incandescent headlamps, they are experiencing a high rate of theft, causing a financial problem and inconvenience to vehicle owners with said HID headlamps in their vehicles. Therefore, it would be very advantageous to provide within an HID headlamp, a circuit that would provide an indication that a stolen HID headlamp does not belong in the vehicle in which it is installed, and does not prevent safe use of the vehicle with the stolen HID headlamp at night.